A leather-like sheet, such as artificial leather, has been used in various applications, such as clothes and materials, because of its flexibility and function not found in natural leather. In view of wearing comfort in clothing use, processability in material use, easy sewing, and appearance of sewn product, much attention has been paid to the elasticity as the most important function.
Therefore, many studies have been carried out on elastically stretchable leather-like sheets. For example, a production method of an artificial leather excellent in the elasticity has been proposed (Patent Document 1), wherein an elastomer sheet which has been stretched in the machine and/or transverse direction by 15% or more is adhesively bonded to an entangled fiber body which is mainly composed of microfine fibers having a single fiber fineness of 0.9 dtex or less and a substrate for artificial leather made of an elastic polymer; the artificial leather is forced to shrink by allowing stretched elastomer sheet to relax; and then the elastomer sheet is removed. However, the proposed production method needs steps of applying an adhesive and removing the adhesive, to reduce the productivity. When the substrate for artificial leather adhesively bonded to the elastomer sheet is forced to shrink, the substrate for artificial leather curls toward the elastomer sheet side, to make the process passing properties poor. Since the substrate for artificial leather is forced to shrink only by the shrinking force of the elastomer sheet, it is difficult to shrink a high-density substrate for artificial leather in a high shrinkage. In addition, the use of an adhesive makes the surface quality of the artificial leather poor.
To eliminate the above drawbacks, a production method free from using an elastomer sheet has been proposed. For example, Patent Document 2 discloses a production method of an artificial leather excellent in stretchability in the transverse direction, in which an artificial leather which is composed of an entangled fiber body mainly including microfine fibers having a single fiber fineness of 1.1 dtex or less and a polyurethane resin is stretched in the machine direction under heating after or simultaneously with the addition of a softening agent, thereby allowing the shrinking in the transverse direction. However, the stretch in the machine direction promotes the unevenness in the mass per unit area and the thickness of the resultant artificial leather. The stretch in the presence of a softening agent results in a suede-finished artificial leather poor in surface uniformity and wear resistance. In addition, the proposed production method is intended to improve the stretchability in the transverse direction of artificial leather. In the proposed production method, since the stretch is made in the machine direction under heating, the obtained artificial leather is less stretchable in the machine direction. Therefore, Patent Document 2 considers nothing about improving the stretchability of artificial leather in the machine direction.
Patent Documents 3 and 4 propose a method of forming wrinkles partly on a fabric or a method of softening a high-density fabric, in which a fabric is forcedly compressed in the machine direction by using a shrinking apparatus which is configured to allow an endless rubber belt to run in contact with a part of the peripheral surface of a heated cylinder roll. However, Patent Documents 3 and 4 describe nothing about artificial leather having an entangled body of microfine fibers and consider nothing about the stretchability of the fabric in the machine direction.
The prior art documents mentioned above do not disclose an easy and efficient method of improving the stretchability and the elasticity of artificial leather in the machine direction. In addition, the prior art documents do not disclose an artificial leather which is improved in the stretchability and the elasticity in the machine direction while the mechanical properties are enhanced by increasing the density.